In the new study, researchers considered three scenarios: that Greenland's present melt rate of 7 percent would continue, or a drop to either one or 3 percent a year—viewed by many as more likely, as the rate is actually expected to slow in coming decades.

"We hope the high end wouldn't happen," said study lead author Aixue Hu of the National Center for Atmospheric Research in Boulder, Colorado.

But "we should be aware that there's a potential the melt of the Greenland ice sheet could be faster than we expected."

Vulnerable

Of the three scenarios, the two lower melt rates are more realistic, according to computer models of future ice sheet melting, Hu said.

A 3 percent melt rate would mean an extra 12 inches (30.5 centimeters) on top of the predicted global sea level rise of 21 inches (54 centimeters), and a one percent rate would mean an extra 8 inches (20.3 centimeters) for the region.